Patent GB-914285-A (GB)
Title: Improvements in the purification of contaminated organic solvents or organic washingliquids
IPC: B01D15/08
Filed: 1959-03-25
Abstract: A rigid foamed absorbent agent in the form of a thermoset condensation product of melamine-formaldehyde, urea-formaldehyde or phenol-formaldehyde is prepared by whipping or beating air or other inert gases into aqueous solutions or suspensions of these condensation products during an intermediate water dispersable stage of polymerization by condensation, e.g. by the method disclosed in U.S.A.  Specifications 2,666,036 or 2,763,475.  The aqueous solution or suspension is prepared from any one of or mixtures of condensation products of melamine-formaldehyde, urea-formaldehyde and phenol-formaldehyde.  In the case of ureaformaldehyde or melamine-formaldehyde products, 1 mol. of melamine or urea is condensed with from about 1,1-1,2 mols. of formaldehyde for each amino group of the melamine or urea, the pH being first adjusted to 5,7-9 with sodium hydroxide or triethanolamine, the mixture being heated with agitation to about 80 DEG C. until all of the urea or melamine dissolves, and cooking being continued until the viscosity thickens to form a syrup of the desired consistency for the subsequent blowing operation. With urea-formaldehyde solutions, the rate of heating is regulated so that the temperature is kept below 80 DEG C. and there is usually required about 30 minutes heating at between 70 DEG -80 DEG C. in order to provide a uniform lower stage of reactive condensation product. In the case of melamine-formaldehyde, after all the melamine has dissolved, it is desirable to carry out the condensation at higher temperature, i.e. at the reflux temperature of the reaction mixture for about 30 minutes.  The end point of condensation in both cases is determined by testing a sample of the syrup and is reached just before a sample gives a precipitate when diluted with an equal volume of water.  At this stage there may be added sodium metabisulphite in a proportion to provide 0,5 mols. of sulphur dioxide for each 2,5 mols. of urea, and the pH is adjusted to pH 5,5-6 after refluxing has been continued for an additional 10 minutes.  The same procedure may be carried out with melamine-formaldehyde resin, an amount of sodium metabisulphite being used which represents 0,5 mol. of SO2 to 3,5 mols. of melamine. Alternatively cationic properties are imparted at this same stage of reaction by adding at the end of the first cooking stage (30 minutes at 80 DEG C. or at reflux, respectively) an amine modifier in an amount of 10% by weight of the urea or melamine, respectively, the amine employed being a polyalkylene-polyamine, e.g. triethylenetetramine, 2-aminopyridine, dicyandiamidine or polyphenylbiguanide (which is a condensation product of aniline, dicyandiamide, formaldehyde and an acid).  The amine modifier is reacted at pH 2-3, the pH being maintained by adding sodium hydroxide as needed until a viscosity of about 100-300 cp is achieved at 25 DEG C.  To prepare a phenol-formaldehyde resin product 94 parts of phenol (1 mol.), 150 parts of 30% aqueous formaldehyde (1,5 mols.) and 9,4 parts of barium hydroxide octahydrate are charged into a reactor. Condensation is conducted at 70 DEG C. for 5 hours.  The product is vacuum concentrated at a temperature not above 70 DEG C. until the resin contains about 35-37% of water.  This is estimated by sampling every 30 minutes and drying the sample at 115 DEG C. for 30 minutes. When the correct figure is reached, the resin is further heated for 4 hours.  The foregoing condensation products are now ready for thickening and whipping or blowing, there being added a hardening catalyst for converting the condensation products by afterheat treatment from an intermediate stage of polymerization to the final solvent-insoluble, water-insoluble thermoset stage. Wetting agents and emulsion stabilizers are added, e.g. alkaryl sulphonates such as Nacconal NR and acid hydrolysed casein, to facilitate foaming.  To facilitate control of the thickening and hardening steps, it is desirable to employ a filler, buffer and curing agent as a unitary addition which is uniformly blended into the resin syrup to provide proper consistency, to minimize shrinkage on the after-heating step and to avoid excess acidity due to acid catalyst used in curing the resin.  Suitable fillers, which may be used in amounts of 5-15% of the resin, are finelydivided wood flour, walnut shell flour, alumina, silica, kieselguhr and fuller's earth, alone or in admixture, and preferably less than 60 mesh to permit uniform mixing.  For addition to the syrup of the phenol-formaldehyde condensation product, a strong organic acid catalyst may be used such as benzoic acid, phthalic anhydride, guanidine persulphate or p-toluene sulphonic acid in an amount of about 1,0-2% by weight of the resin and in this case a buffer is not necessary. Hexamethylene tetramine or paraformaldehyde may also be added in small amounts, e.g. 0,2-0,4 mol. based on weight of resin. Also a base, e.g. calcium oxide or magnesium oxide may be used in amounts of 1-2% by weight of resin. For syrups of urea-formaldehyde and urea-formaldehyde condensation product acidic catalysts, such as an inorganic salt of a weak base and strong acid, are employed as curing catalyst, e.g. ammonium chloride, ammonium sulphate or ferric chloride in an amount of about 0,2-1,2% by weight of the resin, and a buffer, i.e. triethanolamine or tricalcium phosphate, may also be added in amounts of about 1 to 2 times the amount of catalyst.  The buffer may be omitted if desired, particularly in the case of melamine-formaldehyde condensation products.  If desired, the curing step at elevated temperature may be omitted and the products may be foamed by the above discussed technique in which there will be present room temperature curing catalysts such as hydrochloric acid and sodium hydroxide.  These products are not, however, as satisfactory as foamed rigid products cured by baking at elevated temperatures, since the hardening agent is added after foaming and is mixed into the sheet material by spraying directed to both sides of the sheet material which is supported on a foraminous conveyer.  The form of the comminuted particles of synthetic rigid porous open-celled absorbent in accordance with the invention may vary widely.  The particles may be formed as flakes or plates and may be dried on a drum drier and flaked with a knife.  Grinding and chipping may be carried out to provide very large particles, one-half inch or longer in length or finelydivided powder of the order of 100 to 350 mesh.  These particles may be used as adsorbent alone or in admixture with silica gel, kieselguhr, or activated carbon absorbent.ALSO:Contaminated organic solvents containing fatty substances, textile finishing agents and odorous organic substances are filtered through a porous rigid foamed thermoset synthetic resin absorbent of urea-formaldehyde, melamineformaldehyde or phenol formaldehyde.  Said resins may be in the form of a preformed unitary filter element or an assemblage of finely divided or coarse particles.  The resin may be admixed with an inert solvent-insoluble and water-insoluble filler such as finely divided wood flour, walnut shell flour, alumina, silica, kieselguhr or fullers earth.  The porous particles may be used either in the form of a bed or as a suspension in the organic solvent and mechanically separated afterwards.ALSO:A rigid foamed absorbent agent in the form of a thermoset condensation product of melamine-formaldehyde, urea-formaldehyde or phenol-formaldehyde is prepared by whipping or beating air or other inert gases into aqueous solutions or suspensions of these condensation products during an intermediate water-dispersable stage of polymerization by condensation, e.g. by the method disclosed in U.S.A. Specifications 2,666,036 or 2,763,475.  The aqueous solution or suspension is prepared from any one of or mixtures of condensation products of melamine-formaldehyde, urea-formaldehyde and phenol-formaldehyde.  In the case of urea-formaldehyde or melamine formaldehyde products, 1 mol of melamine or urea is condensed with from about 1,1-1,2 mols of formaldehyde for each amino group of the melamine or urea, the pH being first adjusted to 5,7-9 with sodium hydroxide or triethanolamine, the mixture being heated with agitation to about 80 DEG C. until all of the urea or melamine dissolves, and cooking being continued until the viscosity thickens to form a syrup of the desired consistency for the subsequent blowing operation. With urea-formaldehyde solutions, the rate of heating is regulated so that the temperature is kept below 80 DEG C. and there is usually required about 30 minutes heating at between 70-80 DEG C. in order to provide a uniform lower stage of reactive condensation product. In the case of melamine-formaldehyde, after all the melamine has dissolved, it is desirable to carry out the condensation at higher temperature, i.e. at the reflux temperature of the reaction mixture for about 30 minutes.  The end point of condensation in both cases is determined by testing a sample of the syrup and is reached just before a sample gives a precipitate when diluted with an equal volume of water.  At this stage there may be added sodium metabisulfite in a proportion to provide 0,5 mols of sulfur dioxide for each 2,5 mols of urea, and the pH is adjusted to pH 5,5-6 after refluxing has been continued for an additional 10 minutes.  The same procedure may be carried out with melamine-formaldehyde resin, an amount of sodium metabisulfite being used which represents 0,5 mol of SO2 to 3,5 mols of melamine. Alternatively cationic properties are imparted at this same stage of reaction by adding at the end of the first cooking stage (30 minutes at 80 DEG C. or at reflux, respectively) an amine modifier in an amount of 10% by weight of the urea or melamine, respectively, the amine employed being a polyalkylenepolyamine, e.g. triethylenetet